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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 9. (September)

First Page: 1445

Last Page: 1446

Title: Permeability of Clay Shales: ABSTRACT

Author(s): G. Mesri

Article Type: Meeting abstract

Abstract:

Coefficient of permeability is the important material property in the Darcy equation of fluid flow through porous media. Coefficient of permeability is determined by the size of pores, tortuosity of flow channels, porosity, and the nature of the fluid. Mineralogy of shales influences permeability primarily through the size and shape of the particles. Small and filmy particles produce small and highly tortuous pores, whereas large and thick plates or equidimensional grains produce large pores with small tortuosity. The contribution of the fluid to the coefficient of permeability is not limited to the effects of its density and viscosity. The nature of the fluid in which the shale is formed or the fluid that flows through the shale can influence the size, shape, and arrange ent of the particles. In general, the mechanical or physico-chemical mechanisms that promote aggregation increase permeability and those that cause dispersion tend to decrease it. The interaction and bonding of the fluid or organic and inorganic complexes in the fluid with the surface of pores, through such mechanisms as electro-osmotic back-flow, appear to have a secondary influence on the permeability of clays. The effect of the same factors on the permeability of low porosity materials such as shales are unknown.

The observed values of the coefficient of permeability for

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shales are in the range of 10-7 to 10-12 cm/sec. The change in permeability, with void ratio is expressed as ^Dgr log k = ^Dgre/Ck. The parameter Ck is directly related to the void ratio. For clays, values of Ck range from 0.5 to 4. For shales, the Ck values are in the range of 0.02 to 0.5.

Permeability of fissile shales is expected to be highly anisotropic as compared to massive shales that have a more random fabric. However, permeability anisotropy in shales has not been extensively investigated. At shallow depth, the permeability of shale formations is strongly influenced by discontinuities such as fissures and joints.

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Copyright 1997 American Association of Petroleum Geologists